Add option to enable -Wframe-larger-than= on gcc 4.4

Add option to enable -Wframe-larger-than= on gcc 4.4

gcc mainline (upcoming 4.4) added a new -Wframe-larger-than=...
option to warn at build time about too large stack frames. Add a config
option to enable this warning, since this very useful for the kernel.

I choose (somewhat arbitarily) 2048 as default warning threshold for 64bit
and 1024 as default for 32bit architectures.  With some research and
fixing all the code for smaller values these defaults should be probably
lowered.

With the default allyesconfigs have some new warnings, but I think
that is all code that should be just fixed.

At some point (when gcc 4.4 is released and widely used) this should
obsolete make checkstack

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

2 files changed, 15 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 6ae7fd4475b8..c6d331ba140b 100644
--- a/Makefile
+++ b/Makefile
@@ -507,6 +507,10 @@ else
 KBUILD_CFLAGS   += -O2
 endif
 
+ifneq (CONFIG_FRAME_WARN,0)
+KBUILD_CFLAGS += $(call cc-option,-Wframe-larger-than=${CONFIG_FRAME_WARN})
+endif
+
 # Force gcc to behave correct even for buggy distributions
 # Arch Makefiles may override this setting
 KBUILD_CFLAGS += $(call cc-option, -fno-stack-protector)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 623ef24c2381..754cc0027f2a 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -25,6 +25,17 @@ config ENABLE_MUST_CHECK
           suppress the "warning: ignoring return value of 'foo', declared with
           attribute warn_unused_result" messages.
 
+config FRAME_WARN
+        int "Warn for stack frames larger than (needs gcc 4.4)"
+        range 0 8192
+        default 1024 if !64BIT
+        default 2048 if 64BIT
+        help
+          Tell gcc to warn at build time for stack frames larger than this.
+          Setting this too low will cause a lot of warnings.
+          Setting it to 0 disables the warning.
+          Requires gcc 4.4
+
 config MAGIC_SYSRQ
         bool "Magic SysRq key"
         depends on !UML